JPS60207151A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To obtain a sharp print by forming a switching element layer on a conductive substrate, and an electrophotographic sensitive body on this layer and forming a memory image on said photosensitive body even when electrostatic charging and imagewise exposure are executed. CONSTITUTION:The sectional structure is shown here. The switching element layer 2 is formed on a conductive substrate 1, and further, on this layer a charge generating transfer layer or a charge receiving layer 3 is formed. When necessary, a charge injection barrier layer or an under layer for enhancing adhesion or the like layer is sometimes formed between the substrate 1 and the layer 2. The switching element layer 2 convertible to a highly conductive state, when subjected to a high electric field, and capable of retaining this state is used, and it is characterized by this invention.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to electrophotography, and more particularly:
This invention relates to a method of forming a memory image on a photoreceptor using a new principle.

BACKGROUND ART Conventionally, in addition to printing technology, multi-sheet copying technology using electrophotography has come to be used to reproduce multiple sheets of original documents from the viewpoint of ease of operation. A so-called retention-type Wp electroprinting method is known in which, after the photoconductive a photosensitive layer having the multi-moly effect is imagewise exposed, the steps of charging, development, transfer and cleaning are repeated. This method uses the principle that the exposed part of the photosensitive layer becomes conductive due to the photomemory effect, making it difficult for electric charges to be deposited on this part. The sensitivity of the photoreceptor is low, and the photoreceptor must be image-exposed using a high-output light source, which is inconvenient.

Recently, photoreceptors that utilize the optical memory effect have been developed; for example, Professor Bengami et al.
- A photoreceptor coated with a mixed solution of vinylcarbazole (PVK), 2.4.7-trinitrofluorenone < TNF), and a leuco dye on an aluminum electrode, or a photoreceptor coated with a mixed solution of vinylcarbazole (PVK), 2.4.7-trinitrofluorenone < TNF), and a leuco dye, or a mixture of PVK and TNF on the above-mentioned mixture@liquid coating layer. By using a multi-layer photoreceptor provided with a layer of the composition and exposing it to a rotational image, a memory image (decreased charge acceptance in the exposed area) is formed on the photoreceptor, and charging and development are performed. -Research is being conducted to obtain multiple copies by repeating the transfer process (
Japanese Journal of Photography Vol. 44, No. 2, pp. 104-117 (1
981)). Memory formation in these photoreceptors is said to be caused by a chemical reaction after light absorption between a charge transfer complex formed by 1'NF and a leuco dye.

Structure of the Invention According to the present invention, an electrophotographic method is provided in which a memory image is formed by a principle completely different from the memory effect caused by a photochemical reaction. provides a photographic method using an electrophotographic photoreceptor having a novel multi-layer structure with a completely different layer structure.

That is, the present invention provides a conductive substrate, a switching element layer which is provided on a conductive substrate and which becomes and maintains a highly conductive state in a high electric field, and a charge layer provided on the switching element layer. The present invention relates to an electrophotographic method characterized in that an electrophotographic photoreceptor comprising a generation transport layer or a charge receiving layer is charged and imagewise exposed to form a memory image on the photoreceptor.

The present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1 showing the cross-sectional structure of the photoreceptor used in the present invention, a switching element layer 2 is provided on a conductive substrate 1, and a charge generation transport layer or a charge acceptance layer 6 is further provided on this layer 2. provided. Although not shown, a charge injection barrier layer or an underlayer for enhancing adhesion may be provided between the conductive substrate 1 and the switching element layer 2, as desired.

An important feature of the present invention is that the switching element layer 2 is a switching element layer that becomes highly conductive in a high electric field and maintains this highly conductive state.

The principle of forming a memory image and the principle of forming an electrostatic image on a photoreceptor according to the present invention will be explained below with reference to FIGS. 2-A to 2-D.

First, in the charging-image-exposure process shown in FIG. 2-A, the surface of the photoreceptor 40 is charged with a charge Km of a constant polarity by the corona charger 5, and then the surface is image-exposed by the light source 6. In the illustrated example, the surface of the charge-accepting layer 6 is positively charged, and a negative charge is induced in the conductive substrate 1.

In Figure 2-B showing the first stage of memory image formation,
In dark areas, the surface charge is 1/7, but in bright areas,
Charges' (carriers) are generated in the charge-receiving layer 6, and the generated holes (+) move to the lamination interface and the interface with the Tsumugi switching element layer 2 and are accumulated there. At this point, a high electric field is applied to the switching element layer 2.

In Figure 2-C showing the second stage of memory image formation,
In the bright areas of the switching element layer 2, the applied high electric field induces an electrically high conduction state (ON 5TATE), that is, a low resistance state. In the dark part of the switching element layer 2, it remains in a high resistance state (OFF S'l'ATE),
The above-described state is continuously maintained in the switching element layer 2, and as a result, electrons can be easily injected from the conductive substrate 1 in bright areas.

In FIG. 2-D showing the electrostatic image forming process, in the area once exposed to light, electrons (-) that are easily injected into the switching layer 2 in a highly conductive state for subsequent positive charging.
is injected into the charge-accepting layer 6 through the layer 3, reaching the surface and erasing the positive charge (+) on the surface.
A charge image is formed. Although not shown, a copy or printed matter can be obtained by developing this charge image with toner by a method known per se and transferring the formed toner image onto paper or the like. Thus, after one memory image formation shown in FIGS. 2-A to 2-C, the second memory image formation shown in FIGS.
By performing the charging process a desired number of times as shown in FIG. D, it is possible to make a desired number of copies.

As is clear from the above description, the present invention is characterized in that light is used only for the purpose of generating charges in the charge generation and transport layer or the charge transport layer, in other words, for applying a high electric field to the switching element layer 2. I'm worried.

That is, in conventional multilayer photoreceptors, it was necessary to also expose the memory forming layer to light through the charge transport layer or charge receiving layer to cause a photochemical change in the memory forming layer. In the invention, since the charge generating transport layer 1 is required only to generate charges (carriers) in the charge receiving layer, it is possible to form a memory image with a significantly lower exposure amount than in the conventional method. The advantage of this is achieved.

FIG. 6 shows the relationship between applied voltage and current for the switching element layers used in the present invention (Cw, TCNQ described later), and curve 1 shows the relationship between applied voltage and current for the untreated switching element layer. Curve 2, the relationship between voltage and current, is a result of examining a similar relationship for the switching element layer after high voltage application. From curve 1, it can be seen that this switching element has a high resistance state A with a gentle slope and a low resistance state B with an extremely large slope, and curve 2
It is clear that the high resistance state A has almost disappeared in the switching element layer which has once become a high conductivity state (ON 5TATE).

FIG. 4 is a diagram showing the relationship between the blush potential and time of a photoreceptor in which Cv, TCNQ, which will be described later, is used as a switching element layer, and a PVK-TNF complex is used as a charge generation transport layer or a charge reception layer. , curve (1) is the surface charging potential of the untreated photoconductor, curve (2) is the surface charging potential after the start of exposure, and curve (3) is the surface charging potential of the untreated photoreceptor.
) indicates the surface band 'tt position when the photoreceptor whose switching element layer has become highly conductive due to charging exposure is recharged.

In Fig. 4, Vo is the initial charging potential of the photoreceptor equipped with a switching layer in a high resistance state (COFF 5TATE), and Vl is the switching potential in a high conductivity state (ON 5TATE). The switching element layer used in the present invention is in a high resistance state (O
FF 5TATE) electrical resistance (Rm) is 108 to 1
014Ω-al is preferably in the range of io' to 1ollΩ- from the viewpoint of charge retention, and the electric resistance (RL-Ω-c) in the low resistance state (ON 5TETE) of -10,000RH is desirable.
From the viewpoint of contrast, it is desirable that the ratio (A'a/A'r,) to frL) be within the range of 1x10" to 1x10'.

Examples of switching elements having the above-mentioned characteristics include tetracyanoethylene<TCNE), tetracyanoquinodimethane (TCNQ), and tetracyanonaphthoquinodimethane (
TNAP), 2, 6, 5, 6-titrafluoro 7.7
．． 8. '8-tetracyanoquinodimethane (T CN Q
Complexes of electron-accepting substances such as F4 ) with copper or silver are preferably used, but other switching elements with similar properties can also be used.

These complexes can be directly formed in the form of a thin crystalline film on a conductive substrate by means such as vapor deposition, or microcrystals can be dispersed in a resin binder and provided on the conductive substrate. . As the resin binder, electrically insulating resin such as polyester resin, acrylic resin,
Styrene resin, polycarbonate resin, vinyl chloride-vinyl acetate spinning wheel combination, phenoxy resin, ebony resin, silicone resin, alkyd resin, etc. are used. The microcrystalline complex and resin binder are used in a weight ratio of 1:4 to 4:1. These resin binders are dissolved in a solvent such as tetrahydrofuran, chloroform, dioxane, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, etc., the microcrystalline complexes are dispersed, applied onto a conductive substrate, and dried to form a switching element layer. let

The charge generating transport layer or charge receiving layer used in the present invention must be capable of generating charges (>1 carrier) upon irradiation with light, transporting the charges to the interface, and transporting the charges injected from the switching element to the surface. From this point of view, this layer must be capable of transporting both holes and electrons.

For this purpose, mixtures or charge transport complexes of hole transporters and electron transporters are preferably used. Examples of suitable hole transport materials are poly-N-vinylcarbazole, phenanthrene, N-ethylcarbazole, 2,5-diphenyl-1,3,4-oxadiazole, 2,5-bis-
(4-diethylaminophenyl)-1,3,4-oxadiazole, bis-diethylaminophenyl-1,3゜6-oxadiazole, 4,4'-bis(diethylamino-2,2'-dimethyltriphenylmethane) , 2.4.
5-triaminophenylimidazole, 2,5-bis(
4-diethylaminophenyl/I/)-1,3,4-triazole, 1-phenyl-6-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)-2-
Pyrazoline, p-diethylaminobenzaldehyde (
diphenylhydrazone), and examples of suitable electron transport substances are 2-nitro-9-fluorenone, 2,7-sinitro-9-fluorenone, 2.4.7-dolinitro-9
-fluorenone, 2,4,5.7-tetranitro-9-
Fluorenone, 2-nitrobenzothiophene, 2,4.
8-) Linitrothioxanthone, dinitroanthracene, dinitroacridine, dinitroanthraquinone, tetracyanoquinodimethane, and the like.

When these mixtures or complexes have film-forming properties, they can be applied as a solution of an organic solvent onto the switching element layer, and when they do not have film-forming properties, they can be coated with the resin binder exemplified above. The above-mentioned combination material may be dispersed in a bath number and applied to form a charge generation transport layer or a charge acceptance layer.

In the present invention, conductive metal substrates such as copper, aluminum, tinplate, etc., conductive treated paper, NESA glass, etc. are used as the conductive substrate, and these are used in the form of a sheet or a drum.

In the photoreceptor used in the present invention, the thickness of the switching element layer is generally 1 to 5 μm, particularly 1.5 to 3.5 μm.
The thickness of the charge generation/transport layer or the charge transport layer is generally in the range of 6 to 20 μm, particularly 7 to 12 μm, to maintain the surface potential at a high level during charging while maximizing the memory effect. It is preferable for limited use.

In the electrophotographic method of the present invention, by selecting the combination of the switching element layer and the charge generation/transport layer or the charge receiving layer, or the thickness or thickness ratio thereof, the
A memory effect (F) of X or more can be obtained.

In the electrophotographic method of the present invention, the photoreceptor is generally charged using a positive corona charger to a saturated Teiden potential of 500 to 700 volts.

Next, the charged photoreceptor is imagewise exposed. It is a feature of the invention that a conventional electrophotographic light source, such as a Tangesian halogen lamp, can be used as the light source. Although the necessary exposure amount varies depending on the layer structure of the photoreceptor, it is generally recommended to select it from the range of 0.1 to 100 mW/crrL2. Of course, a laser beam such as a gas laser or a semiconductor laser can be used as the light source.

The photoreceptor on which the memory image has been formed is charged directly or by means similar to those described above, and the electrostatic latent image formed is brought into contact with a known one-component or two-component developing toner. The toner image is then transferred to a transfer sheet such as paper and, if necessary, fixed to form a copy or printed matter. After toner transfer, the photoreceptor is electrostatically or mechanically cleaned, and then subjected to the above-mentioned charging, development, transfer, and
Repeat cleaning as many times as necessary.

When forming a new memory image, the switching element layer in the photoreceptor is heated by means such as infrared lamp irradiation, Joule heating, strong laser light irradiation, hot air blowing, or contact with a heated roller. , the switching element layer is returned to the high resistance state B (OFIj' 5TATE), and then the above-described operation is performed.

The heating temperature ranges from 50 to 200°C.

The invention is illustrated by the following example.

Reference Example Formation of Switching Element Layer Copper-tetracyanoquinodimethane complex (Cs/TCNQXO) crushed by a ball mill was mixed with poly77 rylate resin (U-polyner 8000 manufactured by Unitika).
10 parts by weight, polyethylene glycol (PE0 100
(manufactured by Sanyo Chemical Industries, Ltd.) 0.5 parts by weight, chloroform 90
After mixing with a solution consisting of parts by weight and performing ultrasonic dispersion for 60 minutes, the mixture was applied onto a copper substrate using a wire bar and dried. Dry at 80°C for 15 minutes, and if necessary dry for 6 more minutes.
Vacuum drying was performed for 11 q to form a switching element layer with a thickness of 2 μm.

Freeze-11 Constant of Switching Phenomenon Al was vacuum-deposited on the switching element layer, and a sandwich-type cell was formed using the Al-deposited film and the copper substrate as electrodes.

Next, apply +3.0 V to -3, OT/' to the copper board side.
A paper pressure of V- at the first voltage application
One curve is shown in curve (1) in FIG. Furthermore, the V-1 curve in the second and subsequent voltage applications is shown in curve (2).

Preparation of Example Photoreceptor A switching element layer was formed on a t-copper substrate by the same method as in the reference example.

Next, polyvinylcarbazole (Imvican, M
-170 (manufactured by BASF) and 90 parts by weight of tetrahydrofuran to prepare a 10% PVK solution. 0.6 parts by weight of 2.4.5.7-tetranitro-9-fluorenone and 2.0 parts by weight of tetrahydrofuran were added to 10 parts by weight of this 10% PVK solution, and the mixture was dispersed into light components using an ultrasonic dispersion machine to form a photosensitive layer. The coating solution was heated.

This coating solution was applied onto the previously formed switching layer using a wire bar and dried to form a 7 μm photosensitive layer, thereby obtaining a photoreceptor.

Copying Test The entire surface potential of the photoconductor prepared above was set in a photo-attenuation device, and after positive corona discharge (+6.0 KV) was performed for about 60 seconds, the original was exposed. Note that a tungsten lamp (14 mW/cm'') was used as the irradiation light, and exposure was performed for about 1 minute.

Next, the photoreceptor drum of a commercially available electrophotographic copying machine (D (,'-162: manufactured by Sanda Kogyo Co., Ltd.) was replaced with an alumite drum, the exposed photoreceptor was pasted there, and the copper substrate was grounded. Continuously repeat the cycle of post-stop corona discharge (+61 (V)), toner development, transfer cleaning to plain paper,
Electrostatic printing was performed.

When printing was performed up to 50 cycles, almost no image noise or contrast disturbance was observed even when compared with the initial image, and clear printed matter was obtained.

[Brief explanation of the drawing]

Fig. 1 shows the cross-sectional structure of the photoreceptor used in the present invention, Figs. 2-A to 2-D show the principle of forming a memory image and the principle of electrostatic image formation of the photoreceptor used in the present invention, and Fig. 6 The figure shows the relationship between applied voltage and current for the switching element jψ used in the present invention. Figure 4 shows the relationship between position and time on the surface of the photoreceptor used in the present invention◇ 1. Conductive substrate, 2. Switching element layer 6.
...Charge generation and transport or charge acceptance layer Fig. 1 Fig. 3 Fig. 2 F6 IL Fig. 4 g1 Kaku (#)

Claims (1)

[Claims] (1) An electrically conductive substrate, a switching element layer provided on the electrically conductive substrate and capable of attaining and maintaining a highly electrically conductive state in a high electric field, and a charge generation transport layer provided on the switching element layer. An electrophotographic method characterized in that an electrophotographic photoreceptor comprising a charge receiving layer is charged and imagewise exposed to form a memory image on the photoreceptor.